Proton magnetic resonance spectroscopic imaging in newly diagnosed glioblastoma: Predictive value for the site of postradiotherapy relapse in a prospective longitudinal study

Purpose: To investigate the association between magnetic resonance spectroscopic imaging (MRSI)-defined, metabolically abnormal tumor regions and subsequent sites of relapse in data from patients treated with radiotherapy (RT) in a prospective clinical trial. Methods and Materials: Twenty-three examinations were performed prospectively for 9 patients with newly diagnosed glioblastoma multiforme studied in a Phase I trial combining Tipifarnib and RT. The patients underwent magnetic resonance imaging (MRI) and MRSI before treatment and every 2 months until relapse. The MRSI data were categorized by the choline (Cho)/N-acetyl-aspartate (NAA) ratio (CNR) as a measure of spectroscopic abnormality. CNRs corresponding to Tl and T2 MRI for 1,207 voxels were evaluated before RT and at recurrence. Results: Before treatment, areas of CNR2 (CNR >= 2) represented 25% of the contrast-enhancing (TICE) regions and 10% of abnormal T2 regions outside TICE (HyperT2). The presence of CNR2 was often an early indicator of the site of relapse after therapy. In fact, 75% of the voxels within the TICE+CNR2 before therapy continued to exhibit CNR2 at relapse, compared with 22% of the voxels within the TICE with normal CNR (p < 0.05). The location of new contrast enhancement with CNR2 corresponded in 80% of the initial HyperT2+CNR2 vs. 20.7% of the HyperT2 voxels with normal CNR (p < 0.05). Conclusion: Metabolically active regions represented a small percentage of pretreatment MRI abnormalities and were predictive for the site of post-RT relapse. The incorporation of MRSI data in the definition of RT target volumes for selective boosting maybe a promising avenue leading to increased local control of glioblastomas. (c) 2008 Elsevier Inc.